Hi I have installed the Tomcat server and am using Coreservlets book to get along. In chapter 2, section 8 (2.8 Test Your Setup), I'm running into issues.
Basically what I'm doing is this: I've created a servlet that generates the string "Hello" and can be displayed when this servlet is invoked via a browser. I have successfully compiled this servlet (with Eclipse) and deployed my HelloServlet.class into my C:\Program Files\Apache Software Foundation\Tomcat 6.0\webapps\ROOT\WEB-INF\classes directory.
The book you're reading is excellent but is becoming a bit outdated.
It is strongly recommended by most everyone (including the creators of Tomcat) that you never uncomment the Invoker servlet. Instead, start out right from the beginning with explicit servlet mappings in your deployment descriptor.
If a working "Hello, World" app would help you to get acquainted with Tomcat and servlet development, I have one on my site that you can have running in seconds (3 mouse clicks if you've already got Tomcat running on your machnie).